MR D. K. SMYTHE writes: Coward & McClay's (1983) radical reconstruction of S Devon structure depends crucially on the postulate of a major thrust (T1), with a displacement of at least 13 km, invoked to account for the sequence of presumed right-way up older Dartmouth Beds, overlying the younger Meadfoot Group. I suggest that their interpretation of the major structures of the Brixham-Dartmouth area is unlikely, for several reasons:
(1) Their use of bedding-cleavage relationship as a way-up criterion is often unreliable here, where folds are isoclinal or near-isoclinal, and as their fig. 3 shows.
(2) The most northerly exposure of the Dartmouth Beds, 100 m S of the inferred Dartmouth-Meadfoot contact at Kingswear (their critical locality m, grid reference 88245087), reveals downward-facing graded sandstones. In this coastal section bedding and cleavage are parallel, but a number of northerly-overturned, nearly isoclinal folds can be inferred on the basis of sedimentary way-up criteria combined with repetition of lithologies.
(3) Similarly, on the E coast, at Scabbacombe (Coward & McClay's critical locality I), correlation of grit bands and bedding-cleavage geometry suggests that a fold axial plane 100 m S of the Dartmouth-Meadfoot transition is antiformal, and that the contact itself is probably downward-facing; but, as Coward & McClay also note, no reliable sedimentary way-up criteria have been observed here. However, the reconstructed stratigraphic succession, comprising the topmost 300 m (post-flattening) of the Wembury Siltstones (Dineley 1966) of the Dartmouth Beds, can be closely matched to the similar succession S of Kingswear (point (2) above).
